Studies are proposed to conduct a comprehensive examination of oxidative metabolism and function in the normal and postischemic "stunned" myocardium in vivo with transmural metabolic differentiation and over a wide range of energy demands and carbon substrate conditions that occur physiologically. In the last four years, we have conducted extensive studies on the normal and postischemic myocardium using the isovolumic perfused rodent heart model and the non-destructive methods of nuclear magnetic resonance (NMR) spectroscopy. These studies have provided new information and conclusions on respiratory regulation and ischemia-induced alterations in oxidative phosphorylation in the intact myocardium. Studies on perfused rodent hearts by necessity must treat the heart as a homogenous tissue. However, the presence of transmural gradients in oxygen consumption, systolic tension development, and several other aspects of myocardial metabolism are well documented in the normal heart. Similarly, transmural diversity in ischemic damage has previously been noted even in the presence of transmurally uniform perfusion deficit. This diversity is expected to be amplified by transmurally heterogenous hypoperfusion during ischemia induced by partial coronary occlusion. During the last four years we have developed new techniques in surface coil spectroscopy and in spectroscopic spatial localization that will allow, for the first time, a detailed investigation of myocardial bioenergetics and regional function with transmural differentiation in the intact myocardium in vivo. Proposed experiments in the open-chest canine model will examine with transmural differentiation, the regulation of oxidative metabolism in the normal and investigate the alterations induced in oxidative energy metabolism and cardiac function in the reperfused myocardium subsequent to three different types of ischemic insults which result in perfusion-dependent and/or perfusion-independent ischemic damage.